Sudden loss of all electrical power

[68JCode]

My 68 FB has recently developed the annoying habit of losing all electrical power without notice. It has happened 3 times now, and 2 of the three times it came back in less than a minute.

When I say all power, I mean all power - no headlights, no courtesy lights, won't crank, no ignition, nothing!

Any ideas how this happened? I'm assuming there must be a an intermmitant open circuit somewhere between the + post on the relay and the under dash harness. The harness near the relay is a bit of a cut and splice job from the PO, but I've unwrapped about a foot of it and there aren't any fuses or fusible links to be found. There isn't some circuit breaker between the relay and the fusebox is there? Somehow whatever went wrong resets itself.

Obviously I'm a bit nervous taking it back out on the road since it can apparently shut down completely for no earthly reason. There doesn't seem to be any rhyme or reason either - In one case it cut out after driving about 10 minutes on a warm day, and this morning I backed it down the driveway, shut it off, then went to restart it 5 minutes later and no juice. I waited another 30 seconds and it was all back on again!

Thanks,

Andrew

 

[Jonk67]

I've had that problem while driving, everything goes off and the car goes silent, was usually after >15 min. of driving. I had installed an electronic ign. similar to petronix and didn't know there was a resistor in the circuit already, I added another. So as I drove the amount of voltage getting to the coil was less and less until it wasn't enough to fire the rotor or plugs.

The other thing i would check is all of your grounds, make sure they are clean, tight and no paint between the wire and metal. There is a fusible link at the solenoid on the small bolt marked 'S' but that should only be hot during start, shouldn't effect it once running.

Check your battery cables to make sure they aren't corroded internally or fried, if they are rubbery or super stiff they are bad, they should bend and hold shape.

How does the wiring look under the dash at the back of the ign. switch? You might put some graphite in the switch to make sure it turns fully and smoothly.

Next step would be following the wires too/from the fusebox for ign. to see where you have no power when it won't start.
Jon

 

[jims6t6]

My 64 1/2 did that while sitting (read not while driving) It was the solenoid

 

[Mach1Rider]

Complete loss of ALL power is from open ground or positive lead connection.
Check over the battery for poor/dirtyconnections.
Flex the ground wire for stiffness or crackling sounds, (internal corrosion)
Follow the power lead from the starter sol down into the harness inspecting for loose, frayed,corroding connections.

A guess is you will find the power wire under the battery area has some internal problem.

 

[apollard]

If you don't find anything visible, there are connectors in the main power feed inside the harness. One near the solenoid, and one in front of the radiator. When I reworked my harness, mine were pretty burnt.